In forming paper and other sheet materials, twin-wire presses have become popular in recent years. These machines differing from a conventional fourdrinier machine in that the formation of the sheet or web takes place between a pair of wires (often formed of a woven fabric) with dewatering accordingly taking place simultaneously in a pair of opposed directions through both of the wires. In this way it is possible to accelerate the dewatering considerably. As a result of this increased efficiency in the dewatering action, a twin-wire section can be made much shorter and in many ways is more economical than a conventional fourdrinier.
Fabrics for twin wire machines may be “flat-woven” and formed after weaving into an endless belt, or can be woven in endless form. Generally, the flat-woven process is preferred, as it is typically less expensive and more versatile than the endless weaving process.
Of course, flat weaving a fabric requires that provision be made for joining it into endless belts. Such joints should be constructed in such a manner that they are sufficiently strong to withstand the extreme tension, load, temperature, and wear conditions the fabric experiences, yet do not cause the surface of the fabric above the seam to unduly mark the web. One popular method of joining the fabric is to form loops with machine direction (MD) yarns on each end of the fabric. To form the flat-woven fabric into an endless belt, the ends of the fabric are placed adjacent to each other, with each of the loops on one end positioned between two loops on the other end in interdigitating fashion. Once at the location of the twin wire machine, the fabric can be installed by placing it onto the machine, then inserting another (usually more flexible) monofilament pin or pintle into the loops.
Some flat-woven twin wire fabrics have double pin seams formed by the MD yarns. Typically, the MD yarns are looped into either long or short loops, with the long loops projecting farther from the fabric than the short loops. The long and short loops are arranged in a staggered or alternating pattern, such that each long loop has two short loops on either side and vice versa. When the seam is formed by bringing the ends of the fabric together, the long loops of one end of the fabric are aligned with the short loops of the other end of the fabric, such that two different channels are formed by the loops to receive pintles. Double pin seams can typically provide greater strength to the seam at a given thickness than a single pin seam, thereby providing a seam area that is more like the remainder of the fabric.
Installation of the fabric onto a twin wire machine can be a time-consuming operation, particularly in the positioning of the seam loops to receive the pintle. This can be particularly true if the fabric is a double pin seam fabric of the type discussed above, as the seam loops must be carefully aligned so that both pintles can be inserted. Accordingly, it may be desirable to provide a technique that simplifies and/or facilitates installation of seamed fabrics, and in particular double pin seam fabrics.